The present invention relates to hydraulic shock absorbers. More particularly, the present invention relates to an improved hydraulic shock absorber that is adapted for use with motor vehicle suspension systems and that includes additional valving that enhances the dampening characteristics of the shock absorber during low velocity movement of the piston assembly in the recoil or rebound stroke or motion direction.
Hydraulic shock absorbers have long been commonly used in motor vehicle suspension systems to absorb unwanted road caused vibrations that normally occur while the vehicle is being driven. Specifically, shock absorbers are generally connected between the body (the sprung mass) and the suspension (the unsprung mass) of the motor vehicle to dampen vibrations transmitted from the suspension to the body.
Hydraulic shock absorbers usually include a cylindrical tube (frequently known as the inner tube), that defines a cylindrical inner cavity. A piston assembly is slidably disposed in and is reciprocally movable within the inner cavity and serves to divide the inner cavity into two working chambers: a compression chamber; and a rebound chamber, both of which are filled with hydraulic fluid. A fluid reservoir communicates, through valving, with the working chambers, and is usually annularly defined between the inner tube and an outer tube which is concentrically mounted about the inner tube.
One end of the outer or reservoir tube, normally the end adjacent to the compression chamber, is closed by an end cap assembly that is usually connected to the vehicle suspension by a suitable connector. A piston rod extends through a seal assembly and end cap mounted in the other end of the inner tube. The inner end of the piston rod is connected to the piston assembly, and the outer end of the piston rod is connected to the vehicle body by a suitable connector.
The piston assembly typically includes valving that permits fluid to flow across the piston assembly between the working chambers as the piston assembly moves relatively within the internal cavity, that is, relatively with respect to the inner tube. More specifically, the valving limits the flow of fluid across the piston assembly and between the compression and rebound chambers during movement of the piston assembly in a compression stroke direction or in a recoil stroke (sometimes also called the rebound or extension stroke) direction. This provides a damping force that xe2x80x9csmoothesxe2x80x9d or xe2x80x9cdampensxe2x80x9d vibrations transmitted from the suspension to the body. This damping force is, in part, determined by the velocity or speed at which the piston assembly is moved in the inner tube in response to the external forces applied to the shock absorber.
Various different types of valves or valving components have been used with piston assemblies to affect the damping force characteristics of shock absorbers. When a shock absorber piston assembly moves in the recoil stroke direction, these generally include restrictors or restrictor openings, a blow-off valve and orifices or orifice slots. The restrictors are usually holes drilled in the neck of the piston assembly although they may also be drilled in the piston rod. The blow-off valve is usually spring biased closed against a valve seat. The orifices are usually a plurality of rectangular slots coined in the valve seat of the blow-off valve.
During the recoil stroke of a shock absorber, the restrictors are the primary means by which fluid enters the piston assembly from the rebound chamber. Fluid then flows either through the orifice slots, or through the blow-off valvexe2x80x94when that valve""s spring biasing force has been overcomexe2x80x94to the compression chamber. At low velocities of the suspension (that is, at low recoil stroke velocities of the piston assembly) the orifice slots are the primary contributors by way of the damping characteristics. At intermediate recoil stroke velocities of the suspension, it is the blow-off spring""s biasing force that primarily determines the damping characteristics. At relatively high velocities, it is the restrictor openings that determine the damping characteristics. The restrictor openings do, of course, function at all velocities, but the contribution of the restrictors is significantly higher at higher velocities. The contribution of each of these valves or valving components is also dependent on the size of the orifice slots, the diameter of the restrictor openings, and the biasing force on the spring that biases the blow-off valve to a closed position.
Also in the past, some xe2x80x9cpremiumxe2x80x9d shock absorbers had piston assemblies in which additional valving was utilized to provide a more xe2x80x9cplushxe2x80x9d feel at lower operating velocities of the suspension. In these premium shock absorbers, the blow-off valves included valve members, which were spring biased against a valve seat, and in this respect, these valve members were like the valve members used in non-premium shock absorbers. The valve members of the premium-brand shock absorbers were, however, different in that they had an internal thin, flexible disk. This disk normally assumed a flat position and, while in this position, a relatively small flow of fluid was permitted to pass through the blow-off valve member when the blow-off valve was otherwise spring biased closed. This flow through the blow-off valve disk was in addition to the flow through the orifices. Increased fluid flow, resulting from a higher piston assembly velocity, caused the flexible valve disk to assume a flexed, bent or curved position. When in its flexed position, the disk prevented this further fluid flow through the blow-off valve member. The disk assumed its flexed or closed position before the piston assembly velocity caused the blow-off valve to open against the force of its spring bias.
In principal aspects, the improved shock absorber of the present invention includes a further valve that enhances the damping performance of the shock absorber during low velocity movement of the piston assembly in the recoil stroke direction. This novel valve includes a second spring-loaded valve member that normally blocks the flow of fluid past or across the piston assembly downstream, so to speak, from the blow-off valve, that is, after the fluid has flowed through the orifices, and/or through the valve disk that has been used in some premium shock absorbers. This further valve provides an initial firmness to the suspension movement before the blow-off valve opens, and more specifically, offers a firmness vis-a-vis roll stability to the vehicle steering yet provides the desired xe2x80x9cboulevardxe2x80x9d or soft ride that is particularly desired by consumers.
An object of the present invention is to provide an improved shock absorber, as described, where the shock absorber is adapted for connection between the body of a motor vehicle and the suspension of the motor vehicle and serves to dampen vibrations transmitted from the suspension to the body while the vehicle is being driven.
Another object of the present invention is to provide an improved shock absorber, as described, that includes further valving, as described, and that affords advantageous firmness regarding vehicle steering roll stability, together with a boulevard or soft ride, during relatively low velocity movement of the piston assembly in the recoil stroke direction. A related object of the present invention is to provide an improved shock absorber, as described, where the shock absorber includes: an inner tube having a first fluid filled cylindrical internal or inner cavity, that has compression and extension ends and that has a longitudinal central axis extending between the compression and extension ends; a piston assembly that has a longitudinal central axis co-axial with the longitudinal central axis of the inner tube, that has a second internal chamber and a third chamber, that is disposed in and reciprocally moveable, within the internal first cavity, selectively in a recoil stroke direction and in a compression stroke direction, and that serves to divide the internal cavity into a compression and rebound chambers; a restrictor opening for permitting restrictive flow of fluid between the rebound chamber and the second chamber of the piston assembly during movement of the piston assembly in the recoil stroke direction; an orifice for permitting a first predetermined volume of fluid to flow between the second chamber and the third chamber during relatively low velocity movement of the piston assembly in the recoil stroke direction; a blow-off valve that is in the piston assembly between the second chamber and the third chamber, that when opened, permits a relatively large volume of fluid, as compared to the first predetermined volume of fluid flow, to flow from the second chamber to the third chamber, and that is normally biased closed with a first predetermined biasing force; piston rod that has a longitudinal central axis, co-axial with the longitudinal central axis of the inner tube, that has an inner end connected with the piston assembly, and that has an outer end extending out of the extension end of the inner tube; and a further or second valve that is in the piston assembly between the blow-off valve and the compression chamber, that when open, permits a relatively large volume of fluid, as compared to the first predetermined volume of fluid, to flow from the third chamber to the compression chamber, and that is normally biased to a closed position with a second predetermined biasing force, which is less than the first predetermined biasing force, so that the second valve provides an initial firmness to the shock absorber damping before the blow-off valve opens and affords the shock absorber a firmness in regard to the roll stability to the vehicle steering yet providing a relatively soft cushioned or boulevard ride for the vehicle.
A still further object of the present invention is to provide an improved shock absorber, as described, where a first valve seat is defined adjacent to the end of the piston assembly adjacent to the compression chamber, where the second valve includes a second valve member, and where a first coil compression spring biases the valve member against the first valve seat to close the second valve, where the first valve seat is annular, where the first coil compression spring is disposed without the third chamber, where the longitudinal central axes of the first coil compression spring and the inner tube are coaxial, and where the first valve seat is annularly disposed about the longitudinal axis of the piston assembly.
These and other objects, advantages and benefits of the present invention will become more apparent from the following description of the preferred embodiment of the invention taken in conjunction with the following drawings.